This invention relates to golf club shafts, and, more particularly, to a set of golf club shafts having matched natural frequencies of vibration.
The concept of frequency matching golf club shafts is well known, but the methods by which shafts are frequency matched differ. For example, U.S. Pat. No. 3,871,649 describes matching the frequencies of golf club shafts so that the frequency of each shaft is the same. This is accomplished either by using a different wall thickness for each shaft in the set or by varying the lengths of the butt portion and the tip portion of each shaft in the set.
U.S. Pat. No. 4,070,022 describes matching the frequencies of golf club shafts so that a plot of frequency versus shaft length falls along a predetermined gradient. No specific method of achieving frequency matching is described in the patent.
U.S. Pat. No. 4,122,593 describes a method of achieving the frequency matching of U.S. Pat. No. 4,070,022 by removing selected amounts from the butt portion and the tip portion of each shaft.
In accordance with the invention, the frequency of vibration of a set of golf club shafts is matched by varying the length of only one of the stepped portions of each shaft. The length of the remaining stepped portions, the length of the butt portion, and the length of the tip portion remain constant throughout the set. The difference in length of any two shafts corresponds to the difference in length of said one stepped portion of the two shafts. The torsional resistance of the shafts is increased without increasing the weight of the shafts by providing the shafts with relatively large inside and outside diameters and relatively small thicknesses.